The present invention relates to a pulsed laser system, more particulary, to a control circuit for providing variable pulse width control signals to the laser to control its output.
Prior art pulsed lasers use an LC pulse forming network connected to the anode of the tube to store the energy for the laser pulse. A trigger circuit applies a triggering pulse to a coil wrapped around the laser tube which ionizes the argon gas within the tube. This provides a discharge path for the energy stored in the pulse forming network through the laser tube to the cathode causing the tube to lase. However, the laser pulse width is fixed by the LC constant of the PFN. The pulse repetition rate is controlled by the triggering pulses, but the pulse width remains fixed.
When performing perforation procedures such as iridotomies, it is desirable to provide a finite number of high power pulses with predetermined pulse widths. When performing thermal procedures such as coagulation, it is desirable to provide near CW tube operation at relatively low power levels which requires a combination of pulse width and repetition rate to control the energy being delivered. A pulse width which is fixed and optimized for perforation procedures will not in general be optimzed for coagulation procedures.
It is desirable, therefore, to provide a pulsed laser which provides laser pulses with pulse width and repetition rate which vary over a relatively wide range.
When using pulsed lasers in a therapeutic laser system such as in the treatment of the eye, it is also desireable to determine the energy and energy density delivered to the eye during treatment. Because the power of the laser output is adjusted by varying pulse width and repetition rate it is also highly desireable to simplify the requirements of the operator's inputs when using the variable pulse width pulsed laser by providing automatic determination of optimum pulse width.
Finally, it is highly desireable to reduce operator fatigue encountered in lengthy treatment procedures.